Fix warnings

arch/arm/plat-omap/devices.c:159: warning: 'omap_init_kp' 
defined but not used
arch/arm/plat-omap/devices.c:282: warning: 'omap_init_mmc' 
defined but not used
arch/arm/plat-omap/devices.c:436: warning: 'omap_init_wdt' 
defined but not used
arch/arm/plat-omap/devices.c:469: warning: 'omap_init_rng' 
defined but not used

if using omap_2430sdp_defconfig.

Signed-off-by: Dirk Behme <dirk.behme@gmail.com>